Organic semiconductor copolymers containing oligothiophene and n-type heteroaromatic units

ABSTRACT

An exemplary organic semiconductor copolymer includes a polymeric repeat structure having a polythiophene structure and an electron accepting unit. The electron accepting unit has at least one electron-accepting heteroaromatic structure with at least one electron-withdrawing imine nitrogen in the heteroaromatic structure or a thiophene-arylene comprising a C 2-30  heteroaromatic structure. Methods of synthesis and electronic devices incorporating the disclosed organic semiconductors, e.g., as a channel layer, are also disclosed.

RELATED APPLICATION DATA

This application is a divisional of and further claims priority under 35U.S.C. §120 to U.S. application Ser. No. 12/054,134 filed on Mar. 24,2008, which is a divisional of U.S. application Ser. No. 11/073,691filed on Mar. 8, 2005, which claims priority to Korean Application No.10-2004-0053023, filed Jul. 8, 2004, the entire contents of each ofwhich are incorporated herein by reference.

FIELD OF THE DISCLOSURE

The present disclosure generally relates to organic semiconductors. Morespecifically, the present disclosure relates to organic semiconductors,such as thiophene-based π-conjugated polymers, and electronics andstructures incorporating organic semiconductors.

STATE OF THE ART

In the discussion of the state of the art that follows, reference ismade to certain structures and/or methods. However, the followingreferences should not be construed as an admission that these structuresand/or methods constitute prior art. Applicant expressly reserves theright to demonstrate that such structures and/or methods do not qualifyas prior art against the present invention.

Certain alternating single and double bond structures, also calledπ-conjugation, along the backbone of polymer chains can contribute toincreased electron transport and charge storage in such materials. Theπ-conjugation can be along linear structures as well as along aromaticstructures. Examples of π-conjugated polymers includes polyacetylene,polyparaphenylene, polyaniline, polypyrrole and polythiophene. Further,the appending of electron accepting and donating moieties to theπ-conjugated structures can influence the electron transport and chargestorage in such materials.

Organic semiconductors have been used as channel layers in organic thinfilm transistors (OTFT). For example, small molecular organicsemiconductors and polymeric organic semiconductors have been disclosedin U.S. Pat. Nos. 6,107,117; 6,621,099; and 6,723,394; InternationalApplication Publications WO 00/79617 and WO 02/45184; and Mat. Res. Soc.Symp. Proc., vol. 771, L6.1 to L6.5, 157-179 (2003); J. Am. Chem. Soc.Vol. 115, 8716-8721 (1993); and Science, vol. 290, pp. 2130-2133 (2000).

SUMMARY

Exemplary embodiments of the organic semiconductors and methods offorming organic semiconductors disclosed herein are useful forelectronic devices. Further, exemplary embodiments of the disclosedorganic semiconductors have regioregular alternating structuresincluding both p-type oligothiophene and n-type moieties in the mainchain.

An exemplary embodiment of an organic semiconductor copolymer comprisesa poly(oligothiophene-arylene) derivative having a chemical formula:

wherein x is an integer from 3 to 12, y is an integer from 1 to 4 withx>y, R¹ is a hydrogen atom, a C₁₋₂₀ linear, branched, or cyclic alkylgroup, a C₁₋₂₀ alkoxyalkyl group or a C₁₋₁₆ linear, branched, or cyclicalkoxy group, Ar is a C₂₋₃₀ heteroaromatic structure comprising at leastone electron-withdrawing imine nitrogen atom in the heteroaromaticstructure or a thiophene-arylene comprising the C₂₋₃₀ heteroaromaticstructure, and n is an integer from 4 to 200.

An exemplary organic semiconductor copolymer comprises a polymericrepeat structure including a polythiophene structure and an electronaccepting unit, wherein the electron accepting unit includes at leastone electron-accepting heteroaromatic structure having at least oneelectron-withdrawing imine nitrogen in the heteroaromatic structure.

An exemplary embodiment of a method of preparing apoly(oligothiophene-arylene) derivative comprises adding a catalystselected from the group consisting of Pd complexes and Ni complexes to amonomer solution, the monomer solution including a first monomer offormula 1 and a second monomer of formula 2, and preparing thepoly(oligothiophene-arylene) derivative by a polycondensation reaction.Formula 1 is:

wherein A¹ is a halogen atom, a trialkyltin group or a borane group, A²is a halogen atom, a trialkyltin group or a borane group, R¹ is ahydrogen atom, a C₁₋₂₀ linear, branched, or cyclic alkyl group, a C₁₋₂₀alkoxyalkyl group or a C₁₋₁₆ linear, branched, or cyclic alkoxy group,and a is an integer from 1 to 10. Formula 2 is

wherein A³ is a halogen atom or a trialkyltin group, A⁴ is a halogenatom or a trialkyltin group, Ar¹ is C₂₋₃₀ heteroaromatic structurecomprising at least one electron-withdrawing imine nitrogen atom in theheteroaromatic structure or a thiopene-arylene comprising the C₂₋₃₀heteroaromatic structure, and b is an integer from 1 to 4.

An exemplary semiconductor multilayer structure comprises a substrate, agate deposited on the substrate, a source and a drain, the source andthe drain separated from the gate by an insulator, and a channel layerincluding an organic semiconductor. The organic semiconductor comprisesa poly(oligothiophene-arylene) derivative having a chemical formula:

wherein x is an integer from 3 to 12, y is an integer from 1 to 4 withx>y, R¹ is a hydrogen atom, a C₁₋₂₀ linear, branched, or cyclic alkylgroup, a C₁₋₂₀ alkoxyalkyl group or a C₁₋₁₆ linear, branched, or cyclicalkoxy group, Ar is a C₂₋₃₀ heteroaromatic structure comprising at leastone electron-withdrawing imine nitrogen atom in the heteroaromaticstructure or a thiophene-arylene comprising the C₂₋₃₀ heteroaromaticstructure, and n is an integer from 4 to 200.

An exemplary embodiment of a method of preparing apoly(oligothiophene-arylene) derivative comprises adding a catalystselected from the group consisting of Pd complexes and Ni complexes to amonomer solution, the monomer solution including a first monomer and asecond monomer and preparing the poly(oligothiophene-arylene) derivativeby a polycondensation reaction. The first monomer is selected from thegroup consisting of thiophene-distannane, thiophene-diboronate,thiophene-diboronic acid and dihalo-thiophene. The second monomer isselected from the group consisting of a C₂₋₃₀ heteroaromatic structurecomprising at least one electron-withdrawing imine nitrogen atom in theheteroaromatic structure and a C₂₋₃₀ heteroaromatic structurerepresented by:

wherein R² is a hydrogen atom, a hydroxyl group, a C₁₋₂₀ linear,branched or cyclic alkyl group, a C₁₋₂₀ alkoxyalkyl group, or a C₁₋₁₆linear, branched or cyclic alkoxy group, R³ is a hydrogen atom, ahydroxyl group, a C₁₋₂₀ linear, branched or cyclic alkyl group, a C₁₋₂₀alkoxyalkyl group, or a C₁₋₁₆ linear, branched or cyclic alkoxy group, cis an integer from 1 to 8, d is an integer from 1 to 4, and e is aninteger from 1 to 8.

BRIEF DESCRIPTION OF THE DRAWING FIGURES

The following detailed description of preferred embodiments can be readin connection with the accompanying drawings in which like numeralsdesignate like elements and in which:

FIG. 1 illustrates a generalized chemical structure for an exemplaryorganic semiconductor copolymer.

FIGS. 2A and 2B illustrates example chemical structures for organicsemiconductor copolymers that follow the generalized chemical structureof FIG. 1.

FIGS. 3A to 3C illustrate exemplary starting monomers for an exemplaryembodiment of a reaction resulting in the disclosed organicsemiconductor copolymer. FIG. 3A includes the thiophene moiety; FIG. 3Bincludes an electron accepting aromatic moiety, e.g., an n-typeheteroaromatic unit; and FIG. 3C includes a thiopene-arylene.

FIG. 4 illustrates examples of a first type of electron acceptingaromatic moiety.

FIG. 5 illustrates examples of a second type of electron acceptingaromatic moiety.

FIG. 6 illustrates a first exemplary synthesis reaction for an organicsemiconductor copolymer.

FIG. 7 illustrates an exemplary synthesis reaction for a polymersuitable for use as a starting monomer in exemplary reactions to producean organic semiconductor copolymer.

FIGS. 8A to 8C include proton NMR spectra for compound 4 in FIG. 8A andtwo organic semiconductor copolymers -Poly-1 (FIG. 8B) and Poly-2 (FIG.8C).

FIG. 9 schematically illustrates an exemplary embodiment of an organicthin film transistor with a channel layer formed of an organicsemiconductor copolymer disclosed herein.

FIGS. 10A to 10C present experimentally determined source-drain current(I_(SD)) characteristics of organic thin film transistors with a channellayer formed of Poly-1 (FIG. 10A), Poly-2 (FIG. 10B) and Poly-3 (FIG.10C) disclosed herein.

DETAILED DESCRIPTION

Disclosed herein are organic semiconductors and methods of formingorganic semiconductors useful for electronic devices, such as forchannel layer materials in organic thin film transistors (OTFT).

FIG. 1 illustrates a generalized chemical structure 100 for an exemplaryorganic semiconductor copolymer. The FIG. 1 structure 100 includes acertain length of electron-donating (p-type) oligothiophene units 102and an electron-accepting (n-type) moiety 104, which may be a linear ora ring structure.

Any length of electron-donating (p-type) oligothiophene units 102 can bein the structure 100. The number, and therefore the length, of theoligothiophene units 102 contributes to a high p-type behavior for thestructure 100 and contributes to a high on-current, e.g., an on:offratio of greater than 104. P-type behavior general refers to the abilityof the structure to accept positive charge and the ability to delocalizepositive charge among the atoms of the structure, preferably reversibledelocalize the charge. Exemplary electron-donating oligothiophene unitsinclude tetrathiophene, sexithiophene, octothiophene, and so forth.

The FIG. 1 structure 100 also includes an electron-accepting (n-type)moiety 104. N-type behavior general refers to the ability of thestructure to accept negative charge and the ability to delocalizenegative charge among the atoms of the structure, preferably reversiblydelocalize the charge. The number, and therefore the length, of theelectron-accepting moiety 104 contributes to lowering the HOMO level ofthe structure 100 and contributes to a low off-state current, e.g., anoff-state current of less than 10⁻¹¹ amps. Exemplary electron-acceptingmoieties 104 include heteroaromatic structures having at least oneelectron-withdrawing imine nitrogen in the heteroaromatic structure.

The FIG. 1 structure 100 preferably has a regioregular alternatingstructure in the polymer main chain or backbone. Regioregular charactercontributes to dense packing. This dense packing is also known asπ-stacking. In π-stacking, the π-orbitals of the main chain of structure100 are located to overlap π-orbitals of structures in adjacent polymermain chains. When π-orbitals overlap, electrons have higher mobilitybetween polymer main chains, contributing to overall high electronmobility for the structure 100, e.g., greater than 0.05 cm²/Vs.

In a preferred embodiment, the structure 100 is an organic semiconductorcopolymer comprising a polymeric repeat structure including apolythiophene structure and an electron accepting unit, wherein theelectron accepting unit includes at least one electron-acceptingheteroaromatic structure having at least one electron-withdrawing iminenitrogen in the heteroaromatic structure.

The polymeric repeat structure of the exemplary organic semiconductorcopolymer preferably includes at least three polythiophenes structuresand up to 12 polythiophene structures. Also, the exemplary organicsemiconductor copolymer includes from 1 to 4 electron-acceptingheteroaromatic structures. Preferably, the electron accepting unitincludes oligoarylene comprising electronic-accepting heteroaromaticstructures having at least one electron-withdrawing imine nitrogen inthe heteroaromatic structure. The electron-accepting heteroaromaticstructure in preferred embodiments is a C₂₋₃₀ heteroaromatic structureincluding the at least one electron-withdrawn imine nitrogen atom in theheteroaromatic structure or, the electron-accepting heteroaromaticstructure is a thiophene-arylene including the C₂₋₃₀ heteroaromaticstructure.

Further, in exemplary embodiments, the polythiophene structure of thepolymeric repeat structure is functionalized with a side group R¹.Examples of suitable side groups include a C₁₋₂₀ linear, branched, orcyclic alkyl group, a C₁₋₂₀ alkoxyalkyl group or a C₁₋₁₆ linear,branched or cyclic alkoxy group. Further, in preferred embodiments, thenumber of polymeric repeat structures is from 4 to about 20. Inaddition, the number of polythiophene structure, e.g., 3 to 12, isgreater than the number of electron accepting units, e.g., 1 to 4, inthe polymeric repeat structure.

The ratio of polythiophene structures to electron accepting units canvary within the limits described herein and does not have a fixed ratio.However, as the number of electron accepting units increases in thepolymeric repeat unit, the steric hindrance of the polymeric repeatstructure decreases. For example, the steric hindrance where the numberof electron accepting units is 4 is less than the steric hindrance wherethe number of electron accepting units is 3 or less. Furthermore, themore electron accepting units in the polymeric repeat structure, themore positive the overall character of the organic semiconductorcopolymer becomes. In addition, the number of negative moieties, e.g.,the arylene portion of the polymeric repeat structure, improves electronmobility control by influencing the steric hindrance and also improvesthe off-current.

An exemplary embodiment of an organic semiconductor copolymer comprisesa poly(oligothiphene-arylene) derivative having a chemical formula:

wherein x is an integer from 3 to 12, y is an integer from 1 to 4 with xgreater than y, R¹ is a hydrogen atom, a C₁₋₂₀ linear, branched orcyclic alkyl group, a C₁₋₂₀ alkoxy alkyl group or a C₁₋₁₆ linear,branched or cyclic alkoxy group. Ar is a C₂₋₃₀ heteroaromatic structurecomprising at least one electron-withdrawing imine nitrogen in theheteroaromatic structure or a thiophene-arylene comprising the C₂₋₃₀heteroaromatic structure. Typically, n, the number of repeat units inthe copolymer, is an integer from 4 to 200.

The heteroaromatic structure in Ar of Eq. 6 is selected from the groupconsisting of a 5-membered heterocycle and a fused heterocycle. Examplesof suitable five-membered heterocycles include thiazole, thiadiazole,oxazole, isooxazole, oxadiazole, imidazole, pyrazole, triazole, andtetrazole. Examples of fused heterocycles include quinoline,isoquinoline, quinoxaline, naphthridine, benzoimidazole,pyridopyrimidine, benzothiazole, benzothiadiazole, benzotriazole,benzooxazole, phenanthridine, phenanthroline, and phenazine.Furthermore, heteroaromatic structures may be selected from the groupconsisting of pyridazine, pyrimidine, pyrazine, and triazine.

FIGS. 2A and 2B illustrates example chemical structures for organicsemiconductor copolymers consistent with exemplary embodiments disclosedherein. In FIGS. 2A and 2B, twelve example chemical structures are shownlabeled as Poly-1 to Poly-12. Each of the example chemical structures inFIGS. 2A and 2B follow the generic chemical structure of FIG. 1 asdisclosed herein.

An exemplary method of preparing a poly(oligothiophene-arylene)derivative comprises adding a catalyst selected from the groupconsisting of Pd complexes and Ni complexes to a monomer solution. Themonomer solution includes a first monomer containing a thiophene repeatunit along the main chain and a second monomer including an arylenealong the main chain. The method further comprises preparing thepoly(oligothiophene-arylene) derivative by a polycondensation reaction.

The first monomer 120 for the monomer solution is shown in FIG. 3A. Inthe 3A exemplary embodiment, a thiophene repeat unit 122 is positionedalong the backbone chain and is functionalized at a first end bystructure A¹ with a halogen atom, a trialkyltin group or a borane group.The first monomer 120 is also functionalized at a second end bystructure A², which is a halogen atom, a trialkyltin group or a boranegroup. In the first monomer 120, the selection of structure A² may bethe same or independent of the selection of structure A¹. R¹ in thechemical structure illustrated in FIG. 3A represents a hydrogen atom, aC₁₋₂₀ linear, branched or cyclic alkyl group, a C₁₋₂₀ alkoxy alkyl groupor a C₁₋₁₆ linear, branched or cyclic alkoxy group. The number of repeatunits, represented by a, is from 1 to 10.

The second monomer, or arylene monomer, is a C₂₋₃₀ heteroaromaticstructure comprising at least one electron-withdrawn imine nitrogen atomin the heteroaromatic structure or an oliogoarylene comprising the C₂₋₃₀heteroaromatic structure. An exemplary generic structure for this secondmonomer 124 is shown in FIG. 3B. Ar¹ represents the arylene, which ispresent in from 1 to 4 repeat units (represented by b). At a first end,the second monomer 124 of FIG. 3B is functionalized with a halogen atomor a trialkyltin group (A³). At a second end, the second monomer 124 inFIG. 3B is also functionalized independently with a halogen item or atrialkyltin group (A⁴). In the second monomer 124, the selection ofstructure A² may be the same or independent of the selection ofstructure A¹.

In a preferred embodiment, the oligoarylene comprises a C₂₋₃₀heteroaromatic structure. A generic formula for this oligoarylene 130 isshown in FIG. 3C. In the FIG. 3C chemical structure, Ar¹ is a C₂₋₃₀heteroaromatic structure comprising at least one electron withdrawingimine nitrogen atom in the heteroaromatic structure. A³ and A⁴ are thesame as that described for the FIG. 3B chemical structure.

On either end of the oligoarylene 130 of FIG. 3C is a thiophene-basedmoiety 140, 140′. In one exemplary embodiment, a first thiophene moiety140 has an integer number of repeat units where the integer is from 1 to8, e.g., c=1 to 8, and the second thiophene moiety 140′ has an integernumber of repeat units where the integer is from 1 to 8, e.g., e=1 to 8,and the number of arylene repeat units is from 1 to 4, e.g., d=1 to 4.The first thiophene moiety 140 and the second thiophene moiety 140′ areindependently functionalized, represented by R² and R³, respectively. R²is preferably a hydrogen atom, a hydroxyl group, a C₁₋₂₀ linear,branched or cyclic alkyl group, a C₁₋₂₀ alkoxyalkyl group, or a C₁₋₁₆linear, branched or cyclic alkoxy group. R³ is independently a hydrogenatom, a hydroxyl group, a C₁₋₂₀ linear, branched or cyclic alkyl group,a C₁₋₂₀ alkoxyalkyl group or a C₁₋₁₆ linear, branched or cyclic alkoxygroup. In preferred embodiments, the functionalization of the firstthiophene moiety 140 and the second thiophene moiety 140′ are, amongst aplurality of the number of repeat units of first thiophene moiety andsecond thiophene moiety, the same.

Example first monomers and second monomers for synthesis by the methodsdisclosed herein are presented in FIGS. 4A-4C. FIG. 4A shows example5-member heterocycles. FIG. 4B shows example 6-member heterocycles. FIG.4C shows example fused heterocycles. In addition, where the secondmonomer for the synthesis includes a thiophene-arylene comprising theC₂₋₃₀ heteroaromatic structure, examples of oligothiophene derivativessuitable for use in the starting monomer are shown in FIG. 5. Thisfigure includes both 5-membered rings containing a nitrogen as well asfused members containing nitrogen.

In a preferred embodiment, the method prepares the organic semiconductorpolymer by an organometallic polycondensation reaction. FIG. 6 shows anexample of an embodiment of the method disclosed herein. In theexemplary method 200, a bromated arylene 202 (here corresponding to thesecond monomer), forms a mixture with at least one of a first typemonomer 204. As shown in FIG. 6, the first type monomer 204 includes athiophene repeat unit with a halogen atom, a trialkyltin group or aborane group affixed to a first end and/or a second end. Depending uponthe beginning and ending group of the thiophene chain, either apalladium-based catalyst or nickel-based catalyst 206 is added to themixture. For example, palladium-based catalyst typically is used for thecoupling reaction between a halo-arylene and an arylene-trialkylstannane(or -borate; nickel-based catalys typically is used for the couplingreaction of halo-arylenes).

As shown in FIG. 6, multiple synthesis routes 208, 210, 212, 214 areavailable to produce the product organic semiconductor polymer 216. In afirst polymerization method 208, Stille coupling using a palladium-basedcatalyst with thiophene-distannane is used. In this procedure, a mixtureof equal molar equivalents of dibromo-arylene and thiophene-distannaneis formed in anhydrous N,N′-dimethylformamide (DMF) under a nitrogenatmosphere. The DMF is added to about 5 to 10 mole percent oftetrakis(triphenylphosphine)palladium (Pd(PPh₃)₄). The mixture isstirred at 80° C. for 6 to 12 hours. After cooling, the reaction mixtureis filtered and washed with a mixture of dilute aqueous hydrochloricacid in chloroform (NH₄OH(aq)/CHCl₃, and H₂O/CHCl₃), continuously forabout one day. The isolated polymer is filtered by Soxhlet-extractionwith methanol, acetone, and chloroform, in the stated order.

In a second procedure 210, Suzuki coupling using Pd(PPh₃)₄ withthiophene-diboronate is used. In this procedure, a mixture of equalmolar equivalents of dibromo-arylene and thiophene-boronate in tolueneis prepared under nitrogen atmosphere. Into this mixture, about 2 to 10mole percent of Pd(PPh₃)₄ and about 1 molar aqueous solution of aninorganic base, e.g., about 5 to 10 molar equivalents, such as sodiumbicarbonate and potassium bicarbonate, and about 1 to 5 mole percent ofa phase transfer catalyst, such as tetrabutylammonium chloride, is addedand the reaction mixture is then stirred at about 80° C. for 6 to 48hours. The reaction mixture is poured into a mixture of dilute aqueoushydrochloric acid and methanol to precipitate the polymer. Obtainedpolymer is washed with a mixture of dilute aqueous hydrochloric acid andchloroform, continuously fir about one day. The isolated polymer isSoxhlet-extracted with methanol, acetone and chloroform, in the statedorder.

A third synthesis method employs Grignard Metathesis (GRIM) 212 using anickel-based catalyst with dibromo-thiophene. In a preferred example,the nickel-based catalyst is 1,3-Bis(diphenylphosphinoprophane)]dichloronickel (II) (Ni(dppp)Cl₂). In this method, 1.1 molar equivalents ofGrignard reagent (1.0 M solution in diethylether, such asdodecylmagnesiumbromide) is added to a solution of 1.0 molar equivalentof dibromothiophene in anhydrous tetrahydrafurane (THF) at roomtemperature to form a reaction mixture. The reaction mixture is keptunder inert atmosphere. At this point in the procedure, the reactionmixture is a 0.17 M solution against all starting materials havinghalogen atoms, for example dihalo-arylene. The reaction mixture isstirred for 1 to 2 hours at room temperature. A 1.0 M equivalent ofdibromo-arylene and about 0.5 to 10 M percent of a nickel-basedcatalyst, such as Ni(dppp)Cl₂, is added to the reaction mixture. Thereaction mixture is refluxed for about 3 to 6 hours. After that, thereaction mixture is poured into a mixture of dilute aqueous hydrochloricacid and methanol to precipitate the polymer. Obtained polymer is washedwith a mixture of dilute aqueous hydrochloric acid in chloroform,continuously for about one day. The isolated polymer isSoxhlet-extracted with methanol, acetone and chloroform, in the statedorder.

In a fourth embodiment of the disclosed method to form an organicsemiconducting polymer, Yamamoto coupling using a nickel based catalystwith dibromo-thiophene is used 214. In an example of this procedure, amixture of about 1.5 to 2 molar equivalents of zerovalent nickel complex(Ni(0)Lm), e.g., bis(1,5-cyclooctadiene)nickel(0) Ni(cod)₂, and equalmolar neutral ligand (L), e.g. 2,2′-bipyridiyl(bpy), is stirred in thepresence of excess amount of 1,5-cylcooctadiene (cod) in a reactor toform highly-active zerovalent nickel complex, Ni(cod)(bpy). Furtherdetails can be found in T. Yamamoto, et al., J. Am. Chem. Soc., 1994,Vol. 116, p. 4832-4845, the entire contents of which are incorporated byreference. Also present is one molar equivalent of each ofdibromo-thiophene and dibromo-arylene in anhydrous DMF. Stirringcontinues for about 6 to 12 hours at about 60 to 80° C. This procedureresults in precipitation of the polymer. The reaction polymer is thenwashed with a mixture of dilute aqueous hydrochloric acid and chloroformcontinuously for about one day. The isolated polymer is thenSoxhlet-extracted with methylene, acetone and chloroform in the statedorder.

FIG. 7 shows an example monomer synthesis 240 forming a2,2′-Bis(5-bromo-2-thienyl)-5,5′-bithiazole derivative. In the exampleshown in FIG. 7, compound 1 is a 2-thienyl-thiazole derivative, compound2 is a 2-thienyl-5-bromothiazole derivative, and compound 3 is a2,2′-Bis(2-thienyl)-5,5′-bithiazole derivative. Details of the synthesisof this monomer follow.

Compound 1-2-thienyl-thiazole derivative: Compound 1 is prepared ingeneral agreement with the method reported in the literature. See forexample, Dane Goff et al., Tetrahedron Letters, Vol. 40, p. 423-426,(1999). In the case of 4,3′-Dihexyl-(2′-thienyl)-2-thiazole, thesynthetic method began by dissolving 2-Cyano-3-hexylthiophene (10.0 g,51.2 mmol) and Diethylamine (0.4 ml, 4.0 mmol) in DMF(N,N′-Dimethylforamide, 100 mL). At about −80° C., bubbling using H₂Sgas is bubbled through the mixture for about 1 hour to form a crudeintermediate. The crude intermediate (ca. 45 mmol) is then mixed with1-bromo-2-octanone (9.7 g, 50 mmol) in DMF (100 mL) to form a mixtureand the mixture is refluxed for about twelve hours. After reaction thecooled mixture is washed with a mixture of water and chloroform. Columnchromatography in a SiO₂-column using an eluent of hexane/ethyl acetatein a ratio of 20 to 1 results in the product compound 1. In exemplaryembodiments, this reaction has a yield of about 26%. Proton NMR dataCDCl₃ for compound 1 includes δ (ppm) 0.88 (6H), 1.32 (12H), 1.68 (4H),2.73 (2H), 2.83 (1H) 6.92 (1H) and 7.25 (1H).

Compound 2-2-thienyl-5-bromothiazole derivative: In the exemplarymonomer synthesis of FIG. 7, Compound 2 (2-thienyl-5-bromothiazolederivative) is formed in the following manner. A mixture of 17 grams,95.7 mmol of N-Bromosuccinimide (NBS) and 13.1 grams, 95.7 mmol ofcompound 1 are stirred in 200 mL of chloromethane at room temperaturefor about 1 hour. The product recovered from the mixture is washed witha mixture of chloromethane and water and aqueous NaHCO₃. Columnchromatography in a SiO₂-column using an eluent of hexane/ethyl acetatein a ratio of 90 to 1 gives a product in the form of a brown liquid. Inexemplary embodiments, this reaction yields 25.1 grams at a yield of63%. Proton NMR data in CDCl₃ for compound 2 includes δ (ppm) 0.89 (6H),1.35 (12H), 1.68 (4H), 2.73 (2H), 2.83 (2H), 6.92 (1H) and 7.26 (1H).

Compound 3-2,2′-Bis(2-thienyl)-5,5′-bithiazole derivative: Compound 3 ofFIG. 7 is formed in the following manner. Under a nitrogen atmosphere,compound 2 (1.77 grams, 4.28 mmol) is added to a mixture of about 1.5molar equivalents of zerovalent nickel complex (Ni(0)Lm 1:1 mixture ofNi(cod)₂ (1.9 grams) and 2,2′-bipyridiyl(bpy) (1.08 grams) and an excessamount of 1,5-cyclooctadiene (cod) (1 gram) in anhydrous DMF (40 mL).The mixture is stirred at about 80° C. for about 12 to 24 hours.Recovered product is washed with a mixture of aqueous hydrochloric acidand CHCl₃ and water. Column chromatography in a SiO₂-column with aneluent of hexane/ethyl acetate at 8 to 2 ratio gives a product in theform of a red solid. Exemplary synthesis produced 1.13 grams at a yieldof 79%. Proton NMR data in CDCl₃ for this product includes δ (ppm) 0.88(6H), 1.29 (10H), 1.33 (2H), 1.70 (4H), 2.69 (2H), 2.92 (2H), 6.97 (1H),and 7.29 (1H).

Compound 4-2,2′-Bis(5-bromo-2-thienyl)-5,5′-bithiazole derivative:Compound 4 is formed in the following synthesis. A mixture of NBS (1.01grams, 5.7 mmol) and compound 3 are stirred in a mixture of chloroformand acetic acid having a ratio of 30 to 10 by volume at about 25° C. forone hour. The recovered product is washed with a mixture of aqueousNaHCO₃ and water. Column chromatography in a SiO₂-column with an eluentof hexane/ethyl acetate at a ratio of 8 to 2 gives a product in the formof a yellow solid. In exemplary embodiments, 1.3 grams of product wasrecovered at a yield of 58 percent. Proton NMR data in CDCl₃ forcompound 4 is shown in FIG. 8A and includes δ (ppm) 0.88 (6H), 1.31(12H), 1.68 (4H), 2.65 (2H), 2.83 (2H), and 6.92 (1H).

An exemplary embodiment of a polymer synthesis follows. This exemplaryembodiment synthesizes Poly-1, the chemical structure of which is shownin FIGS. 2A and 2B. Exemplary synthesis for Poly-1 includes mixingcompound 4 derivatives from the above disclosed synthesis method formonomers and 5,5′-bis(trimethyltin)-2,2′-bithiophene in anhydrous DMF.In one specific embodiment, 1.0 grams, 1.21 mmol of compound 4 and 0.6grams, 1.21 mmol of 5,5′-bis(trimethyltin)-2,2′-bithiophene was mixedwith 30 mL of DMF under nitrogen atmosphere. To this mixture, about 10mole percent of a palladium catalyst such as Pd(PPh₃)₄ is added. Afterstirring at 80° C. for about 12 hours, the mixture is cooled to roomtemperature. The product is recovered by filtering and washing with amixture of dilute aqueous hydrochloric acid and chloroform, continuouslyfor about one day. The isolated polymer is filtered bySoxhlet-extraction with methanol, acetone, chloroform, in this statedorder. Removal of the solvent and drying recovers a dark red polymer. Inthe specific example disclosed above, 200 mg of product was recovered ata yield of 20 percent. Proton NMR in CDCl₃ of this product is shown nFIG. 8B and includes δ (ppm) 0.92 (12H), 1.30 (20H), 1.44 (4H), 1.74(8H), 2.72 (4H), 2.87 (4H), 7.05 (2H), 7.12 (2H) and 7.18 (2H). In asecond polymer synthesis, Poly-2 was formed. Proton NMR in CDCl₃ forpoly-2 is shown in FIG. 8C and includes δ (ppm) 0.90 (18H), 1.34 (28H),1.43 (8H), 1.74 (12H), 2.71 (4H), 2.81 (4H), 2.91 (4H), 7.02 (4H) and7.09 (4H).

An exemplary embodiment of a semiconductor multilayer structure ispresented in FIG. 9. Exemplary embodiments of a multilayer structure 300comprise a substrate 302, a gate 304 deposited on the substrate 302, asource 306 and a drain 308. The source 306 and the drain 308 areseparated from the gate 304 by an insulator 310. A channel layer 312 isformed in the device of an organic semiconductor polymer. Any organicsemiconductor polymer consistent with the organic semiconductor polymersdisclosed herein are suitable for use as a channel layer. In a specificexemplary embodiment, the semiconductor multilayer structure is ap-channel organic thin film transistor.

An exemplary method to fabricate a semiconductor multilayer structure isas follows. Chromium is deposited onto a washed glass substrate to athickness of 1000 Å by a sputtering process to form a gate electrode.SiO₂ is deposited onto the gate electrode to a thickness of 1000 Å by achemical vapor deposition (CVD) process to form a gate insulatingdielectric layer. A source-drain electrode, for example,indium-tin-oxide (ITO) was deposited onto the gate insulating layer to athickness of 1200 Å by a sputtering process. The resulting structure waswashed with isopropyl alcohol for 10 minutes and dried. The driedstructure was then dipped in a 10 mM octadecyltrichlorosilane solutionin chloroform for 30 seconds followed by washing with acetone anddrying. Subsequently, a channel layer material was deposited on thestructure.

Any suitable solution processing technique can be utilized fordepositing the channel layer. Exemplary embodiments of the disclosedorganic semiconductors have high solubility, e.g., at least 1 and up to2 to 3 weight percent (wt. %) in common organic solvents, such aschloroform, chlorobenzene, toluene, tetrahydrofuran, xylene and thelike. Further, the high solubility of the disclosed organicsemiconductors contribute to improved fabrication methods of electronicand semiconductor devices including the use of solution processtechniques, such as spin coating, dip coating, screen printing, jetprinting, and so forth.

In a specific exemplary embodiment, semiconducting polymer chloroformsolution in a concentration of 1 wt % is applied on the formedsubstrate/source, drain/gate structure by spin coating. Spin coatingoccurred at 1000 rpm and the resulting solution formed a thickness ofabout 1000 Å. The entire structure was then baked under an inertatmosphere at 100° C. for 1 hour resulting in a fabricated organic thinfilm transistor device as shown in FIG. 9.

Comparative Testing. Organic thin film transistor devices utilizingPoly-1, Poly-2, and Poly-3, as shown in FIGS. 2A and 2B, were formed andtested against an organic thin film transistor device utilizing a knownmaterial for the channel layer, e.g., HT-P3HT. Devices for thecomparative example were fabricated as bottom contact devices utilizinga gate electrode of gold, a source and drain electrode of a conductingmaterial, e.g., gold, polysilicon, silver, copper and so forth, a gatedielectric layer of organic polymer film and having a channel width of1000 μm and a channel length of 100 μm. Spin coated film using 1 wt % ofCHCl₃ solution were baked at 80° C. for 12 hours before evaluation. Thedevice evaluation utilized the semiconductor characterization systemdescribed herein with a sweeping range of gate voltage of from minus 60volts to approximately plus 20 volts. Alternatively, for forming thespin coated film, chloroform or chlorobenzene solution can be used at 1wt %.

FIGS. 10A to 10C show the source and drain current characteristics oforganic thin film transistors utilizing Poly-1, Poly-2, and Poly-3,respectively.

Embodiments of devices disclosed herein were evaluated for mobility.Charge mobility was calculated from current-transfer curves of devicesplotted using a Semiconductor Characterization System (4200-SCSavailable from Keithley Corp.). The following current equation wasevaluated in the saturation region:

$\begin{matrix}{I_{SD} = {\frac{{WC}_{o}}{2L}{\mu_{FET}\left( {V_{G} - V_{T}} \right)}^{2}}} & \left( {{Eq}.\mspace{14mu} 7} \right)\end{matrix}$

Where I_(SD) is source-drain current, μ_(FET) is charge mobility, C_(o)is capacitance of the insulating layer, W is channel width, L is channellength, V_(G) is gate voltage and V_(T) is threshold voltage.

Table 1 summarizes results for mobility, on/off ratios, and off-statecurrents for the three inventive devices and the comparative example. Ascan be seen from the results presented in Table 1, the inventive sampleshad a mobility, an on:off ratio, and an off-state current, of from 1 to3 orders of magnitude improved over that of the device using the HT-P3HTmaterial.

TABLE 1 Comparative example Material for Off state current channel layerMobility (cm²/Vs) On:off ratio (A) Poly-1 0.007 to 0.018 6000 1 × 10⁻¹¹Poly-2 0.1   70000 6 × 10⁻¹¹ Poly-3 0.01 to 0.03 10000 1 × 10⁻¹¹HT-P3HT* 0.0008 400 1 × 10⁻⁹  *comparative example: RegioregularHT-poly(3-hexylthiophene-2,5-diyl) commercially available from AldrichCo.

Although the present invention has been described in connection withpreferred embodiments thereof, it will be appreciated by those skilledin the art that additions, deletions, modifications, and substitutionsnot specifically described may be made without department from thespirit and scope of the invention as defined in the appended claims.

1. An organic semiconductor copolymer comprising: a polymeric repeatstructure including a polythiophene structure and an electron acceptingunit, wherein the electron accepting unit includes at least oneelectron-accepting heteroaromatic structure having at least oneelectron-withdrawing imine nitrogen in the heteroaromatic structure. 2.The organic semiconductor copolymer of claim 1, wherein the polymericrepeat structure includes at least three polythiophene structures. 3.The organic semiconductor copolymer of claim 2, wherein the polymericrepeat structure includes from three to twelve polythiophene structures.4. The organic semiconductor copolymer of claim 3, wherein the electronaccepting unit includes from one to four electron-acceptingheteroaromatic structures.
 5. The organic semiconductor copolymer ofclaim 3, wherein the electron accepting unit includes athiophene-arylene comprising the electron-accepting heteroaromaticstructure having at least one electron-withdrawing imine nitrogen in theheteroaromatic structure.
 6. The organic semiconductor copolymer ofclaim 1, wherein the electron-accepting heteromatic structure is a C₂₋₃₀heteroaromatic structure including the at least one electron-withdrawingimine nitrogen atom in the heteroaromatic structure or theelectron-accepting heteroaromatic structure is a thiophene-aryleneincluding the C₂₋₃₀ heteroaromatic structure.
 7. The organicsemiconductor copolymer of claim 1, wherein the polythiophene structureincludes a C₁₋₂₀ linear, branched, or cyclic alkyl group, a C₁₋₁₆linear, branched or, cyclic alkoxy group.
 8. The organic semiconductorcopolymer of claim 1, wherein the number of polymeric repeat structuresis from 4 to about
 200. 9. A method of preparing apoly(oligothiophene-arylene) derivative, the method comprising: adding acatalyst selected from the group consisting of Pd complexes and Nicomplexes to a monomer solution, the monomer solution including a firstmonomer of formula 1 and a second monomer of formula 2; and preparingthe poly(oligothiophene-arylene) derivative by a polycondensationreaction, wherein formula 1 is:

wherein A¹ is a halogen atom, a trialkyltin group or a borane group, A²is a halogen atom, a trialkyltin group or a borane group, R¹ is ahydrogen atom, a C₁₋₂₀ linear, branched, or cyclic alkyl group, a C₁₋₂₀alkoxyalkyl group or a C₁₋₁₆ linear, branched, or cyclic alkoxy group,and a is an integer from 1 to 10, and wherein formula 2 is

wherein A³ is a halogen atom or a trialkyltin group, A⁴ is a halogenatom or a trialkyltin group, Ar¹ is C₂₋₃₀ heteroaromatic structurecomprising at least one electron-withdrawing imine nitrogen atom in theheteroaromatic structure or a thiophene-arylene comprising the C₂₋₃₀heteroaromatic structure, and b is an integer from 1 to
 4. 10. Themethod of claim 9, wherein the thiophene-arylene comprising the C₂₋₃₀heteroaromatic structure is represented by formula 3:

wherein R² is a hydrogen atom, a hydroxyl group, a C₁₋₂₀ linear,branched or cyclic alkyl group, a C₁₋₂₀ alkoxyalkyl group, or a C₁₋₁₆linear, branched or cyclic alkoxy group, R³ is a hydrogen atom, ahydroxyl group, a C₁₋₂₀ linear, branched or cyclic alkyl group, a C₁₋₂₀alkoxyalkyl group, or a C₁₋₁₆ linear, branched or cyclic alkoxy group, cis an integer from 1 to 8, d is an integer from 1 to 4, and e is aninteger from 1 to
 8. 11. The method of claim 10, wherein a plurality ofR² and R³ are the same.
 12. The method of claim 10, wherein the Pdcomplexes are selected from the group consisting of PdL′₄ and PdL′₂Cl₂,wherein L′ is a ligand selected from the group consisting oftriphenylphosphine (PPh₃), triphenylallicin (AsPh₃) andtriphenylphophite (P(OPh)₃).
 13. The method of claim 10, wherein the Nicomplexes are selected from the group consisting of NiL″₂ and NiL″Cl₂,wherein L″ is a ligand selected from the group consisting of1,5-cyclooctadiene, 1,3-diphenylphosphinopropane,1,2-bis(diphenylphosphino)ethane and 1,4-diphenylphopsphinobutane. 14.The method of claim 10, wherein the halogen atom is selected from thegroup consisting of Br, Cl and I.
 15. A semiconductor multilayerstructure comprising: a substrate; a gate deposited on the substrate; asource and a drain, the source and the drain separated from the gate byan insulator; and a channel layer of an organic semiconductor accordingto claim
 1. 16. The semiconductor multilayer structure of claim 15,wherein the semiconductor multilayer structure is a p-channel OTFT. 17.The semiconductor multilayer structure of claim 15, wherein a mobilityis at least 0.007 cm²/Vs.
 18. The semiconductor multilayer structure ofclaim 17, wherein the mobility is about 0.01 to 0.1 cm²/Vs.
 19. Thesemiconductor multilayer structure of claim 15, wherein an on-off ratiois at least
 6000. 20. The semiconductor multilayer structure of claim19, wherein the on-off ratio is from 6000 to 70,000.
 21. Thesemiconductor multilayer structure of claim 17, wherein an off-statecurrent is less than 1×10⁻¹⁰ A.
 22. The semiconductor multilayerstructure of claim 21, wherein the off-state current is from 1×10⁻¹ to1×10⁻¹⁰ A.
 23. A method of preparing a poly(oligothiophene-arylene)derivative, the method comprising: adding a catalyst selected from thegroup consisting of Pd complexes and Ni complexes to a monomer solution,the monomer solution including a first monomer and a second monomer; andpreparing the poly(oligothiophene-arylene) derivative by apolycondensation reaction, wherein the first monomer is selected fromthe group consisting of thiophene-distannane, thiophene-diboronate,thiophene-diboronic acid and dihalo-thiophene, and wherein the secondmonomer is selected from the group consisting of a C₂₋₃₀ heteroaromaticstructure comprising at least one electron-withdrawing imine nitrogenatom in the heteroaromatic structure and a C₂₋₃₀ heteroaromaticstructure represented by:

wherein R² is a hydrogen atom, a hydroxyl group, a C₁₋₂₀ linear,branched or cyclic alkyl group, a C₁₋₂₀ alkoxyalkyl group, or a C₁₋₁₆linear, branched or cyclic alkoxy group, R³ is a hydrogen atom, ahydroxyl group, a C₁₋₂₀ linear, branched or cyclic alkyl group, a C₁₋₂₀alkoxyalkyl group, or a C₁₋₁₆ linear, branched or cyclic alkoxy group, cis an integer from 1 to 8, d is an integer from 1 to 4, and e is aninteger from 1 to
 8. 24. The method of claim 31, wherein the C₂₋₃₀heteroaromatic structure comprising at least one electron-withdrawingimine nitrogen atom in the heteroaromatic structure includes an endgroup selected from the group consisting of halogen atoms.